This topic considers the various ways in which computers can
be connected to each other to communicate, share data and
peripherals.
Four categories of network are covered in the course:
1. LAN
2. WAN
3. Internet
4. Intranet
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In looking at the four categories of networks we will compare
them using the following four characteristics:
a. Transmission media
Refers to the type of cabling or wireless method used to
transfer data.
b. Bandwidth
Relates to the speed at which data can be transferred
throughout the network.
c. Geographical spread
Looks at the size of the area which the network covers.
d. Functions
Considers what tasks the network can carry out for the users.
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1. LAN
2. WAN
3. Internet
http://fcit.usf.edu/network
4. Intranet
a. Transmission media
Fibre-optic cable, Unshielded twisted pair(UTP) cable, co-axial
cable (as used in a tv aerial.)
b. Bandwidth
This depends on the cabling and hardware used. UTP cable
allows data transfer at 10 – 100 Mbps
c. Geographical spread
Physical cabling is laid to connect the network. Usually one
building, school, office, factory. Typically up to about two km.
d. Functions
Peripheral sharing, electronic mail, data sharing.
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1. LAN
2. WAN
3. Internet
4. Intranet
a. Transmission media
Telecommunications systems covering large areas.
b. Bandwidth
Slower than LAN. Depends on the link used. Modem dial-up up
to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.
c. Geographical spread
WANs can cover any size of area. They use
telecommunications which covers most of the earth.
d. Functions
Electronic mail, data sharing, conferencing.
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1. LAN
2. WAN
An internet is a network of networks
3. Internet
4. Intranet
a. Transmission media
Telecommunications systems covering large areas.
b. Bandwidth
Same as WAN. Depends on the link used. Modem dial-up up to
56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.
c. Geographical spread
The Internet can cover any size of area. They use
telecommunications which covers most of the earth.
d. Functions
Electronic mail, information sharing using WWW, File sharing
using FTP.
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1. LAN
2. WAN
3. Internet
An intranet is like the internet but confined to
4. Intranet
one organisation.
a. Transmission media
Telecommunications systems covering large areas.
b. Bandwidth
Slower than LAN. Depends on the link used. Modem dial-up up
to 56 Kbps. ADSL up to 9 Mbps, dedicated line up to 45 Mbps.
c. Geographical spread
Intranet can cover any size of area using telecommunications
links which cover most of the earth. East Dunbartonshire
Council has its own intranet.
d. Functions
Electronic mail, information sharing using WWW, File sharing
using FTP.
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A mainframe is a very large computer which provides
processing power and backing storage facilities to users
working at terminals.
A terminal is a monitor and keyboard with little or no
processing power and no storage facility.
Mainframes were popular for large scale computing ventures
but many have been replaced by newer client server networks.
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Mainframes offer the following facilities:
High capacity input/output. Can access and store data
for thousands of users simultaneously
Powerful processing capability. Can process data for
thousands of users simultaneously
Centralised storage, processing and management of large
amounts of data.
Comprehensive backup, recovery and security for the
system
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Unlike a mainframe, a network is a collection of independent
computers connected together.
Each of the computers has its own processing power and
backing storage capability and is capable of functioning as a
standalone computer.
In the Higher course we will look at two types of network:
1.
Peer-to-peer network.
2.
Client Server network.
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In a peer-to-peer network all the computers have equal status.
Each computer can choose to share its resources with the
other computers. Resources include printers, backing storage
devices, data files.
There is no centralised backing storage as each computer
stores its own data and applications. A system for backups is
therefore difficult to implement.
Security is difficult to maintain as resources, user names
and passwords are not centrally managed.
Most home networks are peer to peer.
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In a Client Server network some computers are clients. People
use these to access the network.
A server is a computer which controls a resource that is made
available to clients on the network. Resources might include
applications, data files, printers, email or internet access.
Backing storage is centralised and all user files are stored on a
file server. It is easy to make backups on the file server.
The server holds a database of all user names, passwords and
access rights. Security is easy to maintain as it is centrally
managed.
The school network is an example of a client server network.
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Advantages of a client-server network
• Backing storage is centralised and all user files are stored on
a file server. It is easy to make backups on the file server.
• The server holds a database of all user names, passwords
and access rights. Security is easy to maintain as it is
centrally managed. Can allow different levels of access for
different users
• Easy to update software as it is done centrally
• Easy to manage and control use of resources such as
printers, internet.
• Reports about users and computer use can be easily generated.
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1. File Server
2. Print Server
3. Web Server
File Server
Stores users’ data files.
Controls file access. Each user has access to certain files.
Controls the type of access. e.g. read only, write, create
Print Server
Handles all printing requests from clients.
Queues jobs, spools them to disk and sends to printer when
printer is ready.
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1. File Server
2. Print Server
3. Web Server
Web Server
Requests for internet access including Web pages, email
and file sharing are dealt with by this server.
Web Server advantages
• Pages can be held locally(cached) which allows faster
access to pages.
• Use of the internet can be monitored more easily when all
internet access goes through the web server.
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The topology of a network refers to the shape of the network,
how the computers are physically connected together.
A node is any device which is attached to the network.
e.g. a computer, printer, server, router.
node
A channel is the way in which data is transferred from
channel
one node to another.
This could a cable or some form of wireless technology.
Network topology diagrams must always be labelled with
the words node and channel
Four topologies are covered in the Higher Course.
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1. Bus
2. Star
3. Ring
4. Mesh
or
node
channel
Used in LANS.
All nodes are connected to a single channel.
A communication from one node is seen by all
the other nodes.
Each node will recognise and accept communications which
are addressed to it.
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1. Bus
2. Star
3. Ring
4. Mesh
or
node
channel
Node Failure
There is typically a mechanism to bypass a failed node
so failure of one node will only affect that node. Rest
of network will still function.
Channel Failure
A channel failure will cause the whole network to fail.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Used in LANS.
Each node has its own channel to the central node.
The whole network depends on the proper functioning of the
central node.
Cabling cost is high because each node has its own
channel but it is easy to extend the network.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Node Failure
A failure of one node will only affect that node. Failure
of the central node will disable the entire network.
Channel Failure
A channel failure will only affect the outer node on
that channel.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Used in LANS.
Channels and nodes form a ring.
Only one node can transmit at a time and data passes
between nodes until it reaches its destination.
The network has to be disrupted when a new node is added.
Designing and extending the network is more difficult than with
a star network.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Node Failure
There is typically a mechanism to bypass a failed node
so a failure of one node will only affect that node.
Channel Failure
A channel failure will disable the entire network.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Used in WANS. e.g. telephone grid.
There are alternative channels between nodes.
Several nodes can transmit at a time and data can be
redirected when some channels are busy.
The extra cabling makes this an expensive type of network
to set up but it is very robust.
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1. Bus
2. Star
3. Ring
4. Mesh
node
channel
Node Failure
The failure of one node will only affect that node.
Channel Failure
A channel failure will have no effect as alternative
channels are available. It may, however, slow down
traffic on the network.
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Some nodes on a network are devices which are there to
manage the flow of data.
When data is sent it includes a destination address.
Each node on the network has its own address to uniquely
identify it.
Three common devices used for managing the flow of data are:
1. Hub
2. Switch
3. Router
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1. Hub
2. Switch
3. Router
Nodes are connected to a hub via channels.
When data is received from a node it is broadcast to all the
other ports.
This is inefficient as the data is intended for only one of the
other nodes.
Stackable hubs with 8, 16 or 24 ports can be linked to form
large LANS.
It may also amplify the signal if long distances are involved.
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1. Hub
2. Switch
3. Router
A switch is sometimes known as an intelligent hub.
When data is received from a node it is examined and then
sent directly to the destination known.
This is more efficient than a hub as the data goes directly
to the destination node.
Switches are more complex than hubs and are therefore more
expensive.
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1. Hub
How can you improve the technical
performance of a network which uses a hub?
2. Switch
3. Router
A Switch would be more efficient than a Hub in that it
doesn’t broadcast data to all nodes on the network
Higher specification cabling could improve technical
performance.
Faster NIC(Network Interface Cards) could also
improve technical performance.
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1. Hub
2. Switch
3. Router
Routers connect different networks together.
They control and manage the flow of data over the different
networks.
They connect smaller networks into larger internetworks.
They connect LANS to telecommunications lines and
the Internet.
They cope with the differences in topologies and transmission
media.
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Each device on a network requires an
interface to allow it to connect.
A Network interface card (NIC) is usually slotted into the
motherboard of the device.
The NIC converts the data to and from a format that can be
transmitted over the network .
Wireless interface cards can also be used.
These can use USB or PCMCIA cards to
allow devices to connect.
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Higher Bandwidth
Technology is improving rapidly and improvements in
bandwidth increase the rate of data transfer.
Higher bandwidth allows the possibility of transferring video,
graphics and audio and will allow live streaming of data.
• Transmit large data files.
• Play network multi-user games with high resolution
graphics.
• Video conferencing.
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Wireless Communications
Wireless communication increases flexibility of use and
is becoming more popular for home, office and public
spaces.
•
No wiring required and ability to move around.
• Can be affected by electrical interference.
• Easy to hack into unless firewall security is enabled.
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There are many technical reasons for the increasingly
widespread use of networks. These include:
• Advances in computer hardware.
• Network interface cards (NIC) are now built into
most computers
• Wireless technology makes it easier to work on
a network.
• Higher bandwidth and faster connection speeds
make networking more attractive
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• Improvements in network related software.
There is a standard protocol for communication – (TCP/IP)
Networking software is now built into common operating
systems e.g. Windows Vista, Linux and Windows XP
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The use of networks which can be local, national or even
international poses legal problems for governments.
Three Acts in particular are relevant for possible
network misuse.
Computer Misuse Act
This Act makes it illegal to breach network security for
any reason.
“Hackers” can be fined or imprisoned for gaining access and
looking at or altering data and also for introducing viruses.
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Copyright, Designs & Patents Act
It is very easy on a network to transfer audio, video and
text at high speed. This has led to a huge increase in the
unauthorised pirating of music, films and books.
This Act makes it illegal to make unauthorised copies of
material.
Offenders can be fined or imprisoned for being involved in this
activity and FAST(The Federation Against Software Theft)
have had many companies and individuals prosecuted.
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Data Protection Act(1998)
http://www.informationcommissioner.gov.uk/
The principles of this Act also apply to network use.
The Act gives individuals(Data Subjects) rights to:
• gain access to their data.
• seek compensation if inaccurate information causes damage.
• "opt-out" of having their data used for direct marketing.
• "opt-out" of fully automated decision-making about them.
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Data Protection Act(1998)
Organisations processing personal data ("controllers") must
comply with the data protection principles. These require data
to be:
• Accurate.
• adequate, relevant and not excessive.
• processed for limited purposes.
• fairly and lawfully processed.
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Data Protection Act(1998)
• processed in accordance with individuals' rights.
• kept secure.
• not kept longer than necessary.
• not transferred to non-EEA (European Economic
Area) countries without adequate protection.
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